Applicant claims priority of Japanese Patent Application Serial No. 2001-149,268, filed May 18, 2001.
The present invention relates to a carburetor and more particularly to an acceleration fuel pump of a float-type carburetor for a combustion engine.
Carburetors for combustion engines are known to have acceleration fuel pumps designed to enrich a fuel-and-air mixture for combustion during acceleration of an engine. Referring to FIG. 7, an acceleration fuel pump 10 of a known float-type carburetor 12 has a body 14 with a float chamber 16. The acceleration pump 10 has a primary machined cylindrical bore 18 carried by the body 14 which intersects a fuel passage 20 that communicates between the float or fuel chamber 16 and a carburetor fuel-and-air mixture passage that typically extends between an air intake filter and the combustion chamber or crankcase of an engine, not shown.
A variable volume fuel reservoir portion of the primary bore 18 is disposed below a reciprocating plunger 24 disposed within the bore 18 and sealably engaging the cylindrical wall. Fuel is drawn into the reservoir portion of the bore 18 from an upstream side of the fuel feed passage 20 when the plunger 24 begins to retract out of the primary bore 18 causing the reservoir portion to enlarge which draws fuel into the reservoir from an upstream side of the fuel feed passage 20. Passage 20 communicates with the fuel chamber 16 of the carburetor 12 through a normally closed inlet check valve 22 disposed in the feed passage and adjacent to the fuel chamber 16 and a normally closed outlet check valve 26 disposed in a downstream side of the feed passage 20. Fuel is drawn into the reservoir by retraction or upward movement of the plunger 24 caused by the force of a compressed spring 28 disposed between the bottom of the plunger 24 and the bottom of the bore 18 and creates a vacuum or subatmospheric pressure which draws or causes fuel to flow into the bore 18. When the running engine begins an acceleration period, a rod 46 engaged to the top of the plunger 24 pushes or advances the plunger against the force of the resilient spring 28 into the fuel filled bore 18. The inlet check valve 22 closes and the outlet check valve 26 opens so that fuel from the reservoir is pushed or flows through the downstream side of the fuel feed passage 20 through the open outlet check valve 26 and into the fuel-and-air mixing passage. When the acceleration of the engine is complete, the spring 28 once again causes the plunger 24 to retract in the bore 18 causing fuel from the fuel chamber 16 to once again fill the expanding reservoir portion of the bore 18.
The inlet check valve 22 has a sleeve 32 press fitted into a machined cylindrical bore in a cavity of the carburetor body 14. The sleeve 32 has a through bore 30 with a seat against which a metallic sphere or ball bearing 34 is forced by a compressed coil spring 36 to bias the check valve 22 closed. The fuel pressure in the upstream side of the bore 30 must be sufficiently greater than the fuel pressure within the primary bore 18 for the net hydraulic force to move the ball 34 away from the seat of the sleeve 32 permitting fuel to flow through the fuel feed passage 20 into the primary bore 18.
The outlet check valve 26 also has a sleeve 40 press fitted into a machine bore 41. However, unlike the inlet check valve 22, a ball bearing 44 is forced against a seat carried by the carburetor body 14 within the bore 41 and below the sleeve 40. When the ball bearing 44 is received on the seat, the check valve 26 is closed and fuel flow into the fuel-and-air mixing passage from the feed passage 20 or air flow into the feed passage 20 from the fuel-and-air mixing passage is blocked. A compression spring 42 is disposed between the sleeve 40 and the ball bearing 44 to yieldably urge the ball bearing against the body seat. During acceleration of the engine and as the plunger 24 is inserted further into the bore 18 the fuel pressure within the fuel feed passage 20 increases moving the ball 44 of the outlet check valve 26 upward and away from the seat against the force of the spring 42 so that fuel can flow into the fuel-and-air mixing passage of the carburetor. When the outlet check valve 26 is open, the inlet check valve 22 remains closed via the ball bearing 34 so that reverse air and/or fuel flow back into the fuel chamber 16 of the carburetor does not occur.
Unfortunately, the construction of the check valves 22, 26 requires additional machining of the carburetor body 14 and requires many component parts which increases manufacturing costs. In addition, dirt and debris can cause malfunction of either check valve which can degrade the efficiency or cause malfunction of the acceleration pump 10.
An acceleration fuel pump of a carburetor for combustion engine is part of the carburetor body and provides an additional flow of fuel to the fuel-and-air mixing passage of the carburetor during acceleration of the engine. The acceleration fuel pump has a plunger which inserts sealably into a cylindrical cavity carried by the body of the carburetor. During acceleration of the engine, the plunger inserts further into the cavity against the resilient force of a spring and toward a resilient check valve member causing the member to deform or expand into a fuel feed state. A fuel feed passage which extends between the bottom of a fuel chamber of the carburetor and the fuel-and-air mixing passage of the carburetor is intersected by the cavity and the resilient check valve member.
A leading portion of the resilient valve member has a slit which opens when the member is in the fuel feed state permitting fuel, displaced by the plunger, to flow out of a fuel reservoir carried by the cavity and into an outlet leg of the fuel feed passage which supplies fuel to the fuel-and air-mixing passage. During insertion of the plunger, pressure within the fuel reservoir overcomes the pressure within the upstream side or inlet leg of the fuel feed passage causing a trailing segment of the member to expand radially outward and engage the internal cylindrical wall of the cavity preventing any reverse flow from the fuel reservoir and into the inlet leg of the fuel passage which extends from the cavity to the fuel chamber. When the engine is done accelerating, insertion of the plunger terminates or has stopped and the internal spring forces the plunger to retract in an outward direction from the cavity. This retraction causes a pressure reduction within the fuel reservoir causing the slit of the leading segment of the check valve member to close and the peripheral rim of the trailing segment to separate or space from the cylindrical wall of the cavity. Fuel then is drawn from the fuel chamber through the inlet leg of the fuel passage into the fuel reservoir in preparation for the next acceleration period of the combustion engine.
Objects, features and advantages of this invention includes an acceleration fuel pump which is significantly impervious to dirt and debris, has a greatly reduced number of parts, requires less machining during manufacturing and may be readily incorporated into existing acceleration fuel pump designs. Additional advantages are improved acceleration of the engine, a relatively simple design and economical manufacture and assembly and in service a significantly increased useful life.